Abstract
This paper briefly outlines the principles of energy extraction from tidal currents and develops a simple model, based upon open channel flow, for the assessment of the influence of such extraction upon the underlying hydraulics. It is shown that energy extraction does alter the flow within a simple channel. Extraction of 10% of the energy flux in a natural, undisturbed channel would produce a flow speed reduction of under 3% rising to 6% for the extraction of 20% of the natural flux. The authors suggest that 10% extraction could be considered as a guideline for developers wishing to make a conservative estimate of the extractable resource in a simple channel.